JPH08220060A - Oxygen sensor - Google Patents

Abstract

PURPOSE: To provide an oxygen sensor which can operate at a low temperature, has a small size, and can easily measure the concentration of oxygen by forming an anode and cathode on the surface of a barium-cerium oxide layer. CONSTITUTION: The electric conductivity of a barium-cerium oxide used for an oxygen sensor element largely fluctuates even in a lean burning region and can detect not only the theoretical air-fuel ratio, but also oxygen even in the lean burning region. In addition, a high-sensitivity sensor can be obtained from the barium-cerium oxide, because the oxide has oxide ion conductivity which is about 100 times as high as that of a zirconium oxide at about 500 deg.C, and the sensor can be used at a low temperature, because the oxide has a sufficiently high oxygen pumping ability at a low temperature of about 20 deg.C. In addition, when such a material as gold having low activity against oxygen is used for the cathode in such a way that gold is used for the cathode and silver is used for the anode, the need of an additional element, such as the resistance plate, etc., can be eliminated by suppressing the dissociation of oxygen on the cathode side. Since silver is used, in addition, the sensor element is stabilized for a long period by reducing the interfacial resistance. Therefore, an oxygen sensor which can operate at a low temperature, has a small size, and can easily measure the concentration of oxygen can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor used for detecting an oxygen concentration in a temperature range from room temperature to a high temperature of about 800 ° C. This oxygen sensor detects oxygen concentration in a living environment, It is used as an oxygen concentration detector for combustion control (lean burn) of combustion equipment such as engines and stoves.

[0002]

2. Description of the Related Art As methods for measuring or detecting oxygen concentration, there are semiconductor type, electrolyte type and the like, roughly classified by materials.
The semiconductor type using a material such as TiO ₂ or SnO ₂ utilizes the fact that the electrical conductivity of the entire oxide bulk changes depending on the oxygen concentration in the gas phase. The conductivity of the n-type TiO ₂ sintered body element at 700 ° C. is proportional to PO ₂ ^−1/4 . Since the conductivity σ changes stepwise with the theoretical air-fuel ratio, it is used for controlling the air-fuel ratio of automobile engines used at high temperatures.
SnO ₂ is attracting attention for complete combustion monitoring of oil stoves and gas stoves, and combustion monitoring of water heaters. In addition, materials such as Co _1-x Mg _x O are also semiconductor type. However, the semiconductor type that changes stepwise at the stoichiometric air-fuel ratio (oxygen concentration of 15% is useful for lean burn control and combustion control of about 15% oxygen concentration, but the oxygen concentration at 15% or more or 15% or less Difficult to grasp and lacks quantitativeness.

On the other hand, the electrolyte type is also classified into a solid electrolyte type and a solution electrolyte type depending on the type of electrolyte. Further, it is classified into a current measurement type and a potential measurement type depending on whether it is detected by the battery current or the battery electromotive force. The solution electrolyte type is
It is generally called a galvanic battery type and is used near room temperature. Therefore, it is not applicable to oxygen sensors at high temperatures such as combustion equipment. Currently, a zirconia-based solid electrolyte type sensor is partially put into practical use as an oxygen sensor at around 800 ° C. or a lean burn sensor for automobile engines. Zirconia-based oxides are chemically stable even in a hydrocarbon gas or a reducing atmosphere, and are high oxide ion conductors, so that they are used in a wide range of fields. Since it is a pure oxide ion conductor, the oxygen concentration can be accurately detected by the electromotive force of the concentration cell. However, in the electromotive force type, the potential change drastically changes at the oxygen concentration of 14.5%, which is the stoichiometric air-fuel ratio, and becomes flat in the lean burn region where the concentration is higher than that.

The limiting current type has attracted attention as a sensor in the lean burn region. It is an electrochemical type that utilizes a cathode reaction, and a constant voltage is applied between both electrodes sandwiching a solid electrolyte, and the current change is read. In the galvanic electrochemical sensor using a solution, a current corresponding to the concentration can be obtained by forming a diffusion layer of the component to be tested on the electrode surface as in the case of polarography. Since the concentration of the product ions is constant, a current change with respect to the oxygen concentration in the gas phase can be obtained by providing a structure in which oxygen in the gas phase on the electrode causes a diffusion layer. The sensor output is linear with the excess air ratio λ,
It has higher sensitivity than semiconductor type and can be used up to high air-fuel ratio. However, the operating temperature is high (700
℃), lowering the operating temperature is an issue.
There is a need for an oxygen sensor that has a simple structure and operates at low temperature. The electrode of the solid electrolyte type sensor has a high temperature (800
Long-term stable platinum is used.

[0005]

As an oxygen concentration detector for detecting the oxygen concentration in the living environment and controlling the combustion (lean burn) of combustion equipment such as an engine or a stove, it is highly sensitive, highly reliable, and small in size. A simple and low-cost sensor is desired. Semiconductor type and limiting current type sensors using conventional oxides including zirconia-based oxides must be operated at high temperatures. Therefore, the test environment is 40
When the temperature is 0 ° C or lower, a heater is required. Further, each of the zirconia and platinum electrodes is stable for a long period of time, but there is a problem that the interface resistance between the zirconia and the platinum electrode is considerably large and the rate of resistance increase is large. Furthermore, in the limiting current formula using platinum-platinum as an electrode, a layer that suppresses oxygen diffusion is required. Therefore, low temperature 200 ℃
Has high conductivity up to the vicinity, and is chemically stable,
Desirably, even a platinum electrode is required to have a solid electrolyte having a small interfacial resistance and a stable electrode for a long period of time. In addition, a sensor that does not require a heater or a resistive plate or a porous layer that suppresses oxygen diffusion is required to reduce the size and cost.

In view of the above problems, it is an object of the present invention to provide an oxygen sensor which can be operated at low temperature, requires no heater, is small in size, is low in cost, and can easily measure oxygen concentration. Another object of the present invention is to provide an oxygen sensor that does not require a resistance plate that suppresses oxygen diffusion and that is small in size, low in cost, and capable of easily measuring oxygen concentration.

[0007]

The present invention provides an oxygen sensor comprising a layer of barium cerium-based oxide, an anode and a cathode formed on the same or different surfaces of said layer. The oxide preferably contains at least one rare earth element as the third element. More preferably, the oxide is of the formula BaCe _1-x M _x O _3- α.
(In the formula, M is La, Pr, Nd, Pm, Sm, Eu, G
at least one rare earth element selected from the group consisting of d, Tb, Dy, Ho, Er, Y and Yb, 0.16
It is an oxide represented by ≦ x ≦ 0.23, 0 <α <1). Among them, M is preferably Gd. In the oxygen sensor according to one aspect of the present invention, the oxide is a conductor of at least one kind of ion selected from the group consisting of a proton and an oxide ion, and the electric conduction of the oxide between the anode and the cathode. It is a semiconductor oxygen sensor that detects the oxygen concentration by changing the temperature. In this semiconductor oxygen sensor, the anode and the cathode may be provided on the same surface of the oxide layer.
An oxygen sensor according to another aspect of the present invention is a limiting current type oxygen sensor in which the oxide is a solid electrolyte and the oxygen concentration is detected by a change in output current when a constant voltage is applied between the electrodes. This limiting current type oxygen sensor has means for suppressing diffusion of oxygen into the solid electrolyte on the cathode side. In this limiting current type oxygen sensor, at least one of the anode and the cathode can be made of platinum or a material containing platinum as a main component. Further, at least one of the anode and the cathode can be made of silver or a material containing silver as a main component.

Further, the present invention comprises a solid electrolyte layer, a cathode and an anode formed on the same surface or different surfaces of the solid electrolyte layer, and the anode is a material containing platinum, silver or one of them as a main component. And a limiting current type oxygen sensor, wherein the cathode is made of gold or a material containing gold as a main component. Further, the present invention provides
A solid electrolyte layer, comprising a cathode and an anode formed on the same or different surfaces of the solid electrolyte layer,
There is provided an oxygen sensor in which the anode is made of silver or a material containing silver as a main component, and the cathode is made of platinum or a material containing platinum as a main component. The present invention also provides an oxygen sensor comprising a solid electrolyte layer, a cathode and an anode formed on the same or different surfaces of the solid electrolyte layer, the cathode being a mixed conductor of electrons (holes) and ions. To do. 90% of the mixed conductor
A dense body having a true density exceeding 10 is preferable.

[0009]

In the present invention, barium cerium oxide is used as the oxide forming the oxygen sensor element. Above all, the formula Ba
Ce _1-x M _x O _3- α (where M is La, Pr, Nd, P
m, Sm, Eu, Gd, Tb, Dy, Ho, Er, Y and Yb, at least one rare earth element, α is an oxygen deficiency, and 0.16 ≦ x ≦ 0.
The oxide represented by 23, 0 <α <1) is an excellent conductor of protons and oxide ions, and therefore effectively functions as an element of a semiconductor type sensor and a limiting current type sensor. That is, in the conventional semiconductor sensor,
It has been utilized that oxides such as TiO ₂ and SiO ₂ change electric conductivity near the stoichiometric air-fuel ratio. However, in the lean burn region, the change in electric conductivity was so small that it could not be used as a sensor. The above oxide has a large change in electric conductivity even in the lean burn region. Therefore, the sensor of the present invention can detect oxygen not only in the stoichiometric air-fuel ratio but also in the lean burn region.

A typical oxide used in the conventional limiting current type oxygen sensor is a zirconia-based oxide, and the conductivity of the oxide ion is about 2 × 10 at 700 ° C. ^{It was −2} S / cm and about 10 ⁻³ S / cm at 500 ° C. On the other hand, the above barium cerium oxide has a high sensitivity sensor because it has an oxide ion conductivity at 500 ° C. which is about 100 times that of zirconia oxide. Further, since it has a sufficient oxygen pumping ability even at a low temperature of about 200 ° C., it can be used at a lower temperature than before. In the limiting current type oxygen sensor, it is usually necessary to provide a means such as a resistance plate for suppressing the diffusion of oxygen on the cathode side. In the oxygen sensor of the present invention, by using a material having a lower oxygen activity than the anode, such as platinum or silver for the anode, gold for the cathode, silver for the anode, and platinum for the cathode, oxygen on the cathode side can be reduced. Dissociation can be suppressed and additional elements such as the resistance plate can be omitted. Further, by configuring the cathode with a mixed conductor of electrons (holes) and ions, it is possible to omit the means for suppressing oxygen diffusion as well. In this case, there is no particular restriction on the anode material.

The present invention also provides a long-term stable oxygen sensor with low interfacial resistance by using silver for the anode or cathode. Heretofore, platinum has been used for the electrodes of oxygen pumps that operate at high temperatures. this is,
Although it is expensive, it is stable at high temperatures of 500 ° C. or higher. However, at a temperature lower than 500 ° C., silver has a higher activity for oxygen and a lower interface resistance with the electrolyte, so that oxygen pumping can be performed smoothly.
Note that silver is difficult to use at temperatures above 800 ° C. As described above, it is possible to manufacture a highly sensitive and highly reliable oxygen sensor that is small, simple, and low cost. When a barium cerium oxide is used as the oxide, the oxygen sensor of the present invention detects the oxygen concentration in the room and controls combustion of combustion equipment such as an engine and a stove in a temperature range from room temperature to a high temperature of about 800 ° C. It can be used as an oxygen concentration detector for (lean burn).

[0012]

EXAMPLES The present invention will be described in detail below with reference to examples. [Embodiment 1] In this embodiment, an example of a semiconductor type oxygen sensor will be described. As barium cerium oxide, Ba
Ce _0.8 Y _0.2 O _3- α or BaCe _{0. 75} Eu _0.25 O _3- α
A disc having a thickness of 0.5 mm and a diameter of 13 mm was used. Platinum electrodes were provided on both sides of this disk. The sensor element was put in an electric furnace, and the atmosphere in the furnace was changed from a nitrogen atmosphere containing 1% oxygen to air under a predetermined temperature, and the resistance change of the oxide element was examined. The results are shown in Table 1 in comparison with conventional zirconia.

[0013]

[Table 1]

The resistance value ratio represents (resistance value in air atmosphere) / (resistance value in 1% oxygen atmosphere). From Table 1,
It can be seen that the barium-cerium oxide has a large change in resistance value due to a change in oxygen concentration, and has a high sensitivity to oxygen. The device of this example has a low temperature of 250 to 300 ° C.
It can be seen that it is about 2 to 4 times more active in oxygen than conventional materials. When the barium-cerium oxide is represented by the formula BaCe _1-x M _x O _3- α, M is Gd, D
It was also found that y, Yb and the like are also highly sensitive to oxygen. When the value of x exceeds 0.4, it is difficult to synthesize an oxide. As is clear from this example, the oxygen sensor using the barium cerium oxide has a higher sensitivity than that using the conventional oxide and can be detected at a low temperature. It will be easy and cheap.

[Embodiment 2] FIG. 1 shows the structure of an oxygen sensor according to the present invention. The oxide 1 is BaCe _0.8 Gd _0.2 which is a mixed ion conductor of a proton and an oxide ion.
O _3- α is used. This oxide is a perovskite type oxide and is thermally stable. Usually, many oxides of this type are unstable in a reducing atmosphere, but they are also stable in a reducing atmosphere. The size of oxide 1 is 10 mm
A platinum electrode 2 having a size of × 10 mm and a thickness of 0.4 mm is provided on both sides of the oxide 1 with the oxide electrode 1 interposed therebetween.

The sensor element was kept at a temperature of 300 to 500 ° C., a test gas of each oxygen concentration was flown, and the characteristics of the sensor were examined. Fig. 2 shows the characteristics at 500 ° C. As a comparative example, the characteristics at 900 ° C. of an oxygen sensor using an oxide semiconductor Co _0.3 Mg _0.7 O are also shown. As can be seen from FIG. 2, by using the oxygen sensor of this example, it is possible to increase the difference in electrical conductivity in the lean burn region at a lower temperature than when the semiconductor Co _0.3 Mg _0.7 O of the comparative example is used. Therefore, it becomes possible to detect the oxygen concentration more accurately. Further, since it can be used at a low temperature, it is judged that it can be used for a wide range of purposes.

[Embodiment 3] FIG. 3 shows the structure of the oxygen sensor of this embodiment. As in Embodiment 2, the oxide 1 has a mixed ion conductor of protons and oxide ions of Ba.
Ce _0.8 Gd _0.2 O _3- α is used. The oxide 1 has a size of 5 mm × 15 mm and a thickness of 0.4 mm, and a pair of platinum electrodes 2 is attached to one surface of the oxide 1.
The sensor element was kept at a temperature of 300 to 500 ° C., a test gas having various oxygen concentrations was flown, and the characteristics of the sensor were examined. FIG.
The characteristics at 500 ° C. are shown together with the characteristics of the sensor of Example 2. It can be seen from FIG. 4 that even if a pair of electrodes are attached to the same surface, the sensor has the same performance as the sensor of the second embodiment. This sensor mounts electrodes on the same surface, so
A simple and high-performance oxygen sensor can be obtained by reducing the manufacturing process of the sensor. In addition, BaCe _0.8 Nd _0.2 O _3- α was added to the oxide.
It was found that the sensor using B.P.O. has a performance equivalent to that of the sensor using BaCe _0.8 Gd _0.2 O ₃ -α.

[Embodiment 4] FIGS. 5 and 6 show the structure of a limiting current type oxygen sensor of this embodiment. The solid electrolyte 11 of the sensor portion is made of BaCe _0.8 Gd _0.2 O ₃ -α sintered body having a size of 10 mm × 10 mm and a thickness of 0.5 mm. A fritless Pt paste obtained by forming a fine platinum powder into a paste with terpineol was applied to both surfaces of the solid electrolyte 11 and baked at 900 ° C. for 1 hour to form an anode 12 and a cathode 13. On the cathode side, a resistance plate 14 made of an alumina plate having a size of 10 mm × 10 mm and a thickness of 0.5 mm for suppressing oxygen diffusion was sealed with a ceramic adhesive 15 leaving a gas inlet having a diameter of 2 mm. 16 and 17 are leads of the anode 12 and the cathode 13, respectively.

The limiting current characteristics of this sensor at various temperatures were examined by the cyclic voltammetry (CV) method. Air, 10% oxygen, and 0% oxygen were each supplied as a test gas in a nitrogen gas balance, and the relationship between the oxygen concentration and the limiting current value was examined. FIG. 7 shows a sensor (a) of the present invention and a comparative example zirconia sensor (b) 500.
The current-voltage characteristics at ° C are shown. It can be seen that the sensor (a) of the present invention is clearly superior to the zirconia type in relative sensitivity. FIG. 8 shows the sensor (a) of the present invention.
The current-voltage characteristics at 200 ° C., 300 ° C., 350 ° C. and 400 ° C. FIG. 8 also shows the current-voltage characteristics of the zirconia sensor (b) at 200 ° C.
It can be seen that the sensor of the present invention can sufficiently detect the oxygen concentration difference with the limiting current even at a low temperature of 200 ° C. In addition, this solid electrolyte BaCe _0.8 Gd _0.2 O ₃ -α is stable in hydrocarbons and reducing gas, and it has been proved in a fuel cell test for 5000 hours.

As is clear from this example, the oxygen sensor using barium-cerium oxide as the solid electrolyte has a higher sensitivity than the conventional zirconia type sensor and can directly detect even at a low temperature, so that it does not require a heater. The structure is simple and inexpensive. Was also measured and the interfacial resistance between the zirconia over platinum electrodes, by an AC impedance method the interfacial resistance between BaCe _0.8 Gd _0.2 O _3- α over platinum electrode. As a result, at 500 ° C., the interface resistance between zirconia and platinum is several MΩcm, while BaCe _0.8 Gd _0.2 O
The interfacial resistance between _3- α and platinum was several tens of Ωcm. Therefore, it is understood that the interface resistance can be suppressed by combining the barium cerium oxide and platinum.

[Embodiment 5] This embodiment is an example of an oxygen sensor using a mixed conductor of electrons (holes) and ions as an electrode. In this sensor, the electrode (cathode) itself has a function of suppressing the conduction of oxide ions, and the oxygen diffusion resistance plate is not necessary. The structure of the sensor is a solid electrolyte with a size of 10 mm × 10 mm and a thickness of 0.5 mm of Ba.
Ce _0.8 Gd _0.2 O ₃ -α sintered body, platinum as the anode, and La _0.5 Sr _0.5 Co _0.8 Mn _0.2 which is a mixed conductor as the cathode.
It was constructed using O ₃ . First, paste powder La _0.5 Sr
_0.5 Co _0.8 Mn _0.2 O ₃ was applied to the solid electrolyte so as to form a thick film, sintered and baked at 1300 ° C., and then the platinum electrode was baked. At this time, the cathode La _0.5 Sr _0.5
Co _0.8 Mn _0.2 O ₃ was a dense electrode having a true density of 92%, and had almost no gas permeation.

The limiting current characteristics were examined by the cyclic voltammetry (CV) method in the same manner as in Example 4.
Air, 10% oxygen, and 0% oxygen were each supplied as a test gas in a nitrogen gas balance, and the relationship between the oxygen concentration and the limiting current value was examined. FIG. 9 shows the sensor (c) 7 of the present invention.
The current-voltage characteristic at 00 ° C is shown. As is clear from this result, the sensor of the present invention can detect the oxygen concentration difference with the limiting current. It can be seen that the oxygen sensor of the present invention using the mixed conductor for the cathode does not require an oxygen diffusion resistance plate and can provide a simple and low-cost oxygen sensor. Similarly, when the current-voltage characteristics of the sensor using 90% of the true density as the cathode were examined, no significant difference in the limiting current density due to the difference in oxygen concentration was observed. It turned out to be difficult.

La _0.4 Sr _0.6 Co _0.8 Fe _0.2 O ₃ , La
_{0.5 Sr 0.5 Co 0.8 Ni 0.2 O} 3, La 0. 5 Sr 0.5 Co 0.6
Similarly, when a mixed conductor such as Cu _0.4 O ₃ was used for the cathode, it was possible to measure the oxygen concentration by the limiting current method without using the oxygen diffusion resistance plate. In the present embodiment, an example is shown in which a mixed conductor of LaSrCoMnO type is used for the electrode, but a mixed conductor of electrons (holes) and ions may be BaSrCoO type or LaBaFeO type.

[Embodiment 6] This embodiment is an example of an oxygen sensor in which the anode and the cathode are made of different electrode materials. In the same manner as in Example 5, a solid electrolyte having a size of 10 mm × 10 mm and a thickness of 0.5 mm BaC was used.
An oxygen sensor was constructed using a sintered body of _0.8 Dy _0.2 O _3- α, platinum as the anode, and gold as the cathode. The limiting current characteristics were examined by the cyclic voltammetry (CV) method in the same manner as in Example 5. As test gas, air,
10% oxygen and 0% oxygen were supplied in a nitrogen gas balance, and the relationship between the oxygen concentration and the limiting current value was examined. FIG. 10 shows current-voltage characteristics of the sensor (d) of the present invention at 500 ° C. As is clear from this result, it is understood that the oxygen concentration difference can be sensed by the limiting current. Owing to the difference in the activity of the electrode surface, the diffusion of oxygen is made different, and the same effect as that when a resistance plate for suppressing the diffusion of oxygen is added to one electrode (cathode) is obtained. It can be seen that the oxygen sensor of the present invention in which the anode and the cathode are made of different electrode materials does not require an oxygen diffusion resistance plate and can provide a simple and low-cost oxygen sensor. Further, in the present embodiment, the case where platinum is used for the anode and gold is used for the cathode is shown, but silver may be used for the anode and gold may be used for the cathode.

[Embodiment 7] This embodiment is an example of an oxygen sensor using silver or a material containing silver as a main component for at least one of an anode and a cathode. In the same manner as in Example 4, the solid electrolyte of the sensor portion had a size of 10 mm × 10.
A stabilized zirconia sintered body containing 8 mol% of yttrium having a thickness of 0.5 mm and a thickness of 0.5 mm was used. A fritless Ag paste in which silver fine powder was made into a paste with terpineol was applied to both surfaces of this solid electrolyte, and baked at 800 ° C. for 1 hour to form an anode and a cathode. On the cathode side,
An oxygen diffusion resistance plate made of a forsterite plate having a size of 10 mm × 10 mm and a thickness of 0.5 mm was sealed with glass 5 leaving a gas intake port of 2 mm.

The interfacial resistance of the electrode at this time was measured by the AC impedance method and compared with that of the conventional platinum electrode. At 800 ° C. and 700 ° C., no remarkable difference in interfacial resistance was observed, but it was found that the difference increased at 600 ° C. or lower. The results of the Cole-Cole plots of the platinum electrode and the silver electrode at 500 ° C. are shown in FIG. The vertical axis of FIG. 11 represents resistance (number of lies), and the horizontal axis represents resistance (real number). As is clear from FIG. 11, the interface resistance of the silver electrode is smaller. Further, when the life cycle was examined by repeating the heat cycle of room temperature → 500 ° C. → room temperature 200 times for 1000 hours, the interfacial resistance was increased by 7% for the platinum electrode, while it was about 1% for the silver electrode. It was As described above, it is clear that the silver electrode has a smaller interfacial resistance than the platinum electrode with respect to the zirconia-based solid electrolyte, has high sensitivity, and has excellent long-term stability. Also, when using BaCe _0.8 Gd _0.2 O ₃ -α sintered body as the solid electrolyte,
Similar results are obtained, which shows that the silver electrode is superior to the platinum electrode.

In Examples 4 to 7, B was used as the solid electrolyte.
aCe _0.8 Gd _0.2 O ₃ -α, BaCe _0.8 Dy _0.2 O ₃ -α,
An example using a zirconia-based solid electrolyte was shown.
BaCe _0.8 Y _0.2 O ₃ -α or BaCe _0.8 Tb _0.2 O ₃ -α may be used. In addition, a solid electrolyte such as a ceria type, a hafnia type, or a bismuth type, which is used in this type of limiting current type oxygen sensor, can be used. Of course, the platinum, silver, and gold electrodes used in the examples may be a mixture with other components. In addition, the synthesis and manufacturing methods of the electrolyte and the mixed conductor include coating method, vapor deposition method, sputtering method, C.I. V. The D method or the like may be used.

[Embodiment 8] In this embodiment, BaCe, which is a mixed ion conductor of a proton and an oxide ion in an oxide, is used.
_0.8 Nd _0.2 O _3- α is used. The oxide has a size of 5 mm × 15 mm and a thickness of 0.4 mm, and a pair of silver electrodes is attached to one surface of the oxide. The configuration of the sensor is the same as that of the third embodiment except for the electrodes. The sensor element was kept at a temperature of 300 to 500 ° C., a test gas having various oxygen concentrations was flown, and the characteristics of the sensor were examined. FIG. 12 shows the characteristics of the sensors of this Example and Example 3 at 500 ° C. It can be seen from FIG. 12 that even if silver is used as the electrode, it has the same performance as the sensor using platinum. In this example, BaCe _0.8 Nd _0.2 O ₃ -α, which is a mixed ionic conductor of protons and oxide ions, was used as the electrolyte. And BaCe _0.9 Gd _0.1 O _3- with different amounts of substitution
It is also possible to use α, BaCe _0.9 Y _0.1 O ₃ -α, or the like.
Further, the pair of electrodes need not be the same, and Pt, Ag, Au, or the like can be used as the electrode material.

[0029]

According to the present invention, it is possible to realize a highly sensitive and highly reliable oxygen sensor which is small, simple, and low cost. INDUSTRIAL APPLICABILITY The oxygen sensor of the present invention is particularly excellent in detecting the oxygen concentration near a low temperature of 200 ° C., and is small, simple, and low cost as an oxygen concentration detector for combustion control (lean burn) of combustion equipment such as engines and stoves To do.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an oxygen sensor according to a second embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between oxygen partial pressure and electric resistance of the oxygen sensor.

FIG. 3 is a vertical sectional view of an oxygen sensor according to a third embodiment.

FIG. 4 is a diagram showing a relationship between oxygen partial pressure and electric resistance of the oxygen sensor.

FIG. 5 is a vertical sectional view of a limiting current type oxygen sensor in Example 4.

FIG. 6 is a plan view of the oxygen sensor.

FIG. 7 is a diagram showing a comparison of current-voltage characteristics at 500 ° C. of the sensor of Example 4 and the zirconia sensor.

FIG. 8 is a diagram showing a comparison of current-voltage characteristics at 200 ° C. between the sensor of Example 4 and the zirconia sensor.

9 is a diagram showing current-voltage characteristics at 700 ° C. of the sensor of Example 5. FIG.

FIG. 10 is a diagram showing current-voltage characteristics at 500 ° C. of the sensor of Example 6.

FIG. 11 is a diagram showing Cole-Cole plots of a platinum electrode and a silver electrode of the sensor of Example 7 at 500 ° C.

FIG. 12 is a diagram showing a relationship between oxygen partial pressure and electric resistance of an oxygen sensor in Example 8.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunihiro Tsuruta 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Nobuhisa Ito 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (13)

[Claims] 1. An oxygen sensor comprising a layer of barium cerium oxide, an anode and a cathode formed on the same or different surfaces of said layer. 2. The oxygen sensor according to claim 1, wherein the oxide contains at least one rare earth element as a third element. 3. The oxide has the formula BaCe _1-x M _x O _3- α.
(In the formula, M is La, Pr, Nd, Pm, Sm, Eu, G
at least one rare earth element selected from the group consisting of d, Tb, Dy, Ho, Er, Y and Yb, 0.16
The oxygen sensor according to claim 2, wherein the oxygen sensor is an oxide represented by ≦ x ≦ 0.23, 0 <α <1). 4. The oxygen sensor according to claim 3, wherein M is Gd. 5. The oxide is a conductor of at least one ion selected from the group consisting of protons and oxide ions, and oxygen changes due to a change in electrical conductivity of the oxide between the anode and the cathode. The oxygen sensor according to claim 1, which detects a concentration. 6. The oxygen sensor according to claim 5, wherein the anode and the cathode are provided on the same surface of the oxide layer. 7. The oxygen sensor according to claim 1, wherein the oxide is a solid electrolyte, and the oxygen concentration is detected by a change in output current when a constant voltage is applied between the electrodes. 8. The oxygen sensor according to claim 7, further comprising means for suppressing diffusion of oxygen into the solid electrolyte on the cathode side. 9. The oxygen sensor according to claim 7, wherein at least one of the anode and the cathode is made of silver or a material containing silver as a main component. 10. An oxygen sensor comprising a solid electrolyte layer, a cathode and an anode formed on the same or different surfaces of the solid electrolyte layer, the cathode being a mixed conductor of electrons (holes) and ions. 11. The oxygen sensor according to claim 10, wherein the mixed conductor is a dense body having a true density of more than 90%. 12. A solid electrolyte layer, a cathode and an anode formed on the same surface or different surfaces of the solid electrolyte layer, wherein the anode is made of platinum, silver, or a material containing one or more as a main component. An oxygen sensor whose cathode is made of gold or a material whose main component is gold. 13. A solid electrolyte layer, a cathode and an anode formed on the same surface or different surfaces of the solid electrolyte layer, wherein the anode is made of silver or a material containing silver as a main component, and the cathode is platinum or An oxygen sensor made of a material whose main component is platinum.